Producing rubber mixtures in combination master batch and final mixer utilizing ram- and ram-less kneaders

ABSTRACT

A method and apparatus for producing rubber mixtures in two stages, namely a master-batching stage and a final mixing stage, with the maximum temperature during final mixing being less than the maximum temperature during master batching. In order to reduce the overall mixing time, and in order to simplify the mixing apparatus, the material that is to be mixed is passed successively through a master batcher and then a final mixer. The material that is to be mixed is transferred or conveyed from the master batcher to the final mixer via the force of gravity without intermediate storage thereof. After the master batching, the material that is to be mixed is cooled in the final mixer. During cooling and final mixing of a first charge in the final mixer, master batching of a subsequent charge is already effected in the master batcher. The master batcher and the final mixer are expediently combined in such a way that the master batcher is a ram kneader, and the final mixer is a ram-less kneader.

BACKGROUND OF THE INVENTION

The present invention relates to a method of producing rubber mixturesin two stages, namely a master-batching stage and a final mixing stage,with the maximum temperature during final mixing being less than themaximum temperature during master batching. The method may also be adiscontinuous method that uses kneaders, with material that is to bemixed passing successively through the kneaders. The present inventionalso relates to an apparatus for carrying out the aforementionedmethods.

Of particular significance during the manufacture of rubber articles isthe production of vulcanizable rubber mixtures from the necessarycomponents, namely rubber, fillers, and other additives, and from thecomponents that are necessary for vulcanization or bonding. Next to theunits for vulcanization, the units needed for mixing and preparationrepresent the greatest investment in a rubber plant. Internal mixers areprimarily used to manufacture such mixtures.

The mixing process performs two different tasks:

(a) on the one hand, the additives that are necessary in order toprovide the preparation and usage properties, such as, for example,highly active and other fillers, plasticizers, processing aids,anti-oxidants, ozone protectors, pigments, etc., must be dispersed asrapidly and as effectively as possible. In this connection, dependingupon the mixing unit that is used, the type of mixture, and the mixingconditions, temperatures of up to 150° C. and even greater can beachieved during master batching without damaging the mixture; and

(b) on the other hand, however, the materials that are necessary forpolymerization and bonding to substrates, such as, for example, sulfurand vulcanization accelerators, peroxides, vulcanization resins,RF-systems, etc., must be added in at such low temperatures that in sodoing no premature reactions occur. With moist accelerator and bondingsystems, the temperatures may not exceed 100° to 110° C. during finalmixing.

Where larger quantities have to be dealt with, especially in the tireindustry, a two-stage process is therefore used for the mixing. First ofall, the additives are added to the rubber at relatively hightemperatures; this is the master batching. The mixture is then cooled ina recovery unit and subsequently in air or water, and is finallyintermediately stored. Then, in a second stage, the materials that arenecessary for polymerization and bonding to substrates are added at atemperature that is lower than the master batch temperature; this is thefinal mixing. During such final mixing, the temperature must be lowenough that the rubber does not already begin to polymerize in themixer.

The manner in which the heretofore known mixing process carries outthese two stages entails expensive transportation within the plant area,increases the occurrence of unusable residual quantities, and requires adosing of the respective mixture components prior to both stages of theprocess.

In order to avoid these drawbacks, so-called single-stage kneadingprocesses have been developed where the two decisive stages of theprocess, namely the master batching and the final mixing, accompanied bythe interposition of a cooling process, are effected one after the otherwithin a single unit. However, kneaders that operate in this fashionwork too slowly. For the large quantities that are required to be dealtwith in tire plants, several of these kneaders must be installedparallel to one another. Thus, these kneaders would require aninvestment that is too great, and would require too much space in aplant.

It is therefore an object of the present invention to shorten theoverall mixing time, and to simplify the mixing apparatus.

BRIEF DESCRIPTION OF THE DRAWINGS

This object, and other objects and advantages of the present invention,will appear more clearly from the following specification in conjunctionwith the accompanying schematic drawings, in which:

FIG. 1 is a view that schematically illustrates one exemplary embodimentof the inventive apparatus for carrying out the method of the presentinvention; and

FIG. 2 is a vertical cross-sectional view through one exemplaryembodiment of the inventive apparatus for carrying out the method of thepresent invention.

SUMMARY OF THE INVENTION

Pursuant to one inventive variant, the method of the present inventionis characterized primarily by the steps of: having the material that isto be mixed pass successively through a master batcher and then a finalmixer, including conveying the material that is to be mixed from themaster batcher to the final mixer via the force of gravity without theintermediate storage thereof; after the master batching, cooling thematerial that is to be mixed in the final mixer; and during cooling andfinal mixing of a first charge in the final mixer, effecting masterbatching of a subsequent charge in the master batcher. Thus, pursuant tothe present invention, the master batcher and the final mixer areexpediently combined in such a way that the master batcher is a ramkneader, and the final mixer is a ram-less kneader.

Pursuant to another inventive variant, the method of the presentinvention may be characterized primarily by the steps of: havingmaterial that is to be mixed pass through a first kneader that is in theform of a ram kneader and forms a master batcher; conveying the materialthat is to be mixed, without intermediate storage thereof, from thefirst kneader to a second kneader, which is in the form of a ram-lesskneader and forms a final mixer; after the master batching, cooling thematerial that is to be mixed in the second kneader, which is larger thanthe first kneader; and during cooling and final mixing of a first chargein the second kneader, effecting master batching of a subsequent chargein the first kneader.

In contrast to the so-called single-stage process, which should actuallybe called a single-unit process, with the present invention considerabletime is saved by the contemporaneous master batching and final mixing.The combination unit that operates pursuant to the present inventionmakes it possible, by specializing the final mixer for cooling and finalmixing, to have a throughput of material that is to be mixed that is atleast as rapid as was possible with two single-unit mixer that operatedparallel to one another. However, the inventive combination of the twomixers into a single apparatus is considerably simpler and lessexpensive, because in so doing only one of the two kneaders, namely themaster batcher, has to be an expensive ram kneader. Furthermore, onlythe master batcher has to have the enormous power and capability that isrequired to plasticize a cold rubber mixture, whereas the final mixerhas only to be designed for plasticizing the finished master batch,which is at approximately 100° C., and hence is considerably moreflowable. For this reason, the final mixer expediently has at most 30%of the power of the master batcher.

Shortening the initial cooling phase that is effected in the final mixerhelps to further accelerate the process. This shortening of the coolingphase is made possible by having the cooling surfaces of the final mixerbe 10 to 60%, and preferably 15 to 50%, greater than the surfaces of themaster batcher. This can be achieved either by a particularly closearrangement of the blades of the final mixer, and/or by having theoverall final mixer larger, i.e. with a greater capacity, than themaster batcher. The mixers may be provided with cooling channels,whereby the least thickness between the cooling channels and those wallsurfaces that face the material which is to be mixed is expedientlysmaller for the final mixer than for the master batcher. This feature ispermitted by a low mechanical stressing of the final mixer, and providea particularly low resistance to the transfer of heat from the materialthat is to be mixed to the cooling channels in the blades and the casingof the final mixer.

Final mixing is advantageously accelerated by effecting the addition ofthe polymerizing material and/or the reactive materials that serve forthe bonding on the substrates, which addition takes place at thebeginning of the final mixing, in such a way that this material ormaterials are distributed over the free surface of the material that isto be mixed. In contrast to the concentrated application of additivethat up to now has been customary, the inventive surface application ofadditive provides a higher degree of uniformity right from thebeginning. This improvement is made possible by the ram-less design ofthe final mixer.

The amount of time that the material that is to be mixed stays in thefinal mixer can be reduced even further if the polymerization agentsand/or the reactive materials that serve for the bonding on thesubstrates, all of which are added at the beginning of the final mixer,are preliminarily dispersed only coarsely in the final mixer, and aresubsequently finely dispersed in a roller mechanism, or in a single ordouble mixing screw. In the aforementioned listing, the threealternative mixing mechanisms are arranged in order of their capacity.When the inventive method is used in plants that consume a lot ofrubber, where the present invention is particularly applicable becausethere the accelerated throughput of rubber has the greatest effect, thedouble mixing screw is preferred due to its large capacity.

In order to protect the operating personnel from organic vapors that areinjurious to health, and to keep dirt away from the material that is tobe mixed, transfer of this material from the master batcher to the finalmixer is expediently effected in such a way as to be sealed from, orexclude, dust and air. Such an exclusion is particularly easy to realizewith the ram-less configuration of the final mixer because themaster-batched material can pass directly into the final mixer from thechannel that is sealed against dust and air. The channel construction isparticularly straightforward if no mechanical power has to be introducedfrom the outside for the transfer of the material that is to be mixed.For this reason, it is advisable to place the master batcher as highabove the final mixer as possible, and also to offset the master batcherat an angle from the final mixer at least to such an extent that theforce of gravity alone is sufficient to overcome all frictionalresistances that are encountered during the transfer of the materialthat is to be mixed from the master batcher to the final mixer. Inaddition, arranging the mixers one above the other reduces the amount ofspace that is required.

In contrast to the heretofore known two-stage process, the presentinvention eliminates the need for transferring the material that is tobe mixed from the master batcher kneader to the intermediate depositsite, and then from the latter to the final mixing kneader, and hencealso eliminates the space that is required for intermediate storage.Also eliminated is the heretofore required weighing or dosing of themaster batch prior to the final mixing. For operation, it is now merelynecessary to have a kneader operator and one other operator.Furthermore, instead of two complete kneader units, two preparationunits, and two batch-off units, it is now merely necessary to have asingle kneader unit, a second mixing casing, and only a singlepreparation unit and a single batch-off unit. Since with the presentinvention the master batching and the final mixing are effected attemperatures greater than ambient temperature, the previously requiredenergy consumption for plasticizing prior to final mixing is eliminated.Last but not least, cleaning costs are lower with the present invention,because not only one preparation unit but also one batch-off unit areeliminated; a change of mixtures is thus facilitated.

It is, of course, also possible to initially add non-reactive materialsin the lower kneader.

The material that is to be mixed is expediently discharged from thelower kneader into a roller mechanism or a single or double mixing screwdisposed therebelow, whereupon the material is further processed in acustomary manner. A mixing screw, and especially a double mixing screw,is advantageous because it does not limit the size of the mixingapparatus, especially not even if packing mechanisms are used to chargethe unit. In such units, which are well known, an excellent dispersionof the components of the mixture can be achieved at relatively lowtemperatures.

Subsequently, a strip, for example a tread rib, is extruded and isprocessed or dressed in the customary batch-off units.

During the mixing process, the temperature and the energy input aremeasured in both kneaders, and the mixing process is controlled on-line.Furthermore, it is advisable to use characterizing data from the mixingscrew, and from the mixed material that exits therefrom, such as, forexample, extrusion expansion, surface quality, etc., again for on-linecontrol. This makes it possible to limit the quality control to merelydetermining the vulcanization characteristics and data.

Further specific features of the present invention will be described indetail subsequently.

DESCRIPTION OF PREFERRED EMBODIMENTS

Referring now to the drawings in detail, FIG. 1 shows a press or ramkneader 1 that is provided for producing a master batch and is disposedat the top. The arrow 2 indicates the flowing-in of the master batchcomponents. As indicated by the arrow 3, the finished master batch isconveyed by the force of gravity into the ram-less kneader 4 withoutbeing intermediately stored. In this stage of the process, the speed ofthe kneader is so low that a very rapid cooling-off is achieved. Afterthe mixture has been cooled to below the critical temperature, which formost accelerator systems is between 100° and 110° C., the reactivematerials are added, as indicated by the arrow 5. The vulcanizable finalmixture is formed by dispersion. As indicated by the arrow 6, thisvulcanizable final mixture is discharged into a worm mixer 7. Tofacilitate this step, the lower kneader 4 can be tilted, as indicated bythe hinge joint 8.

As shown by the exemplary embodiment illustrated schematically in FIG.1, the method of the present invention provides a very compactconstruction without the need for intermediate storage, which wouldrequire more space and would also utilize transport capability.

Referring now to the apparatus of FIG. 2, the ram kneader 1 is providedat the top with a working cylinder 9 for raising and lowering a press orram 10, which in FIG. 2 is disposed in its upper end position to allowthe mixing chamber 13 to be charged with the master batch components.These components are added in the direction of the arrow 2 via a hopper12. After charging has been completed, the ram 10 is lowered until itcloses off the top of the mixing chamber 13, which is provided with tworotors 14. In a manner known per se, the sides of the mixing chamber 13are closed off by casing parts 15. These parts, and the rotors disposedtherein, can have a conventional construction, and in particular arealso equipped with suitable cooling devices.

The bottom of the mixing chamber 13 is closed off by a saddle 17 thatcan be opened and closed by the working cylinder 16; the top 17' of thesaddle extends into the mixing chamber 13. After the master batch iscompleted, the mixing chamber 13 is emptied from the bottom by openingthe saddle 17. In so doing, the master batch is discharged from themixing chamber 13 directly into the mixing chamber 19 via thecontinuously open, i.e. ram-less, inlet 18 thereof. The mixing chamber19 of the kneader 4 is also provided with two rotors 20. In comparisonto the ram kneader 1, the mixing chamber 19 of the kneader 4 isconsiderably larger. Furthermore, the rotors 20 operate at a relativelylower speed in order to assure that the aforementioned cooling of thematerial that is to be mixed occurs. After the reactive materials havebeen added in the direction of the arrow 5, the final mixture iswithdrawn by opening the hinged saddle 21 of the kneader 4 toward thebottom; the top 21' of the saddle extends into the mixing chamber 19.The final mixture is then processed further in the manner described inconnection with FIG. 1.

During the time that the mixture is being processed in the kneader 4,the next charge is already being prepared in the ram kneader 1. Shouldthe capacity of the kneader 1 be too great, or the capacity of thekneader 4 be too small for the aforementioned operations, a secondkneader 4 could be installed. The two kneaders 4 would then preferablybe disposed next to one another in order to be able to selectivelycharge one or the other of the adjacent kneaders 4. This splitting-up ofthe material that is to be mixed to two kneaders 4 can be accomplishedin a simple manner by disposing a pivotable deflector below the ramkneader 1.

The present invention is, of course, in no way restricted to thespecific disclosure of the specification and drawings, but alsoencompasses any modifications within the scope of the appended claims.

What I claim is:
 1. A method of producing rubber mixtures to save timeby contemporaneous master batching and final mixing in two stages,namely a master-batching stage having a ram kneader and a final mixingstage having a ram-less kneader including a continuously open ram-lessinlet, with the maximum temperature during final mixing being less thanthe maximum temperature during master batching; said method incombination comprises the steps of:first passing the material that is tobe mixed successively through a master batcher having enormous powercapability required to plasticize a cold rubber mixture and then a finalmixer having at most 30% of power of the master-batching stage andadapted only for plasticizing the finished master batch which is atapproximately 100° C. and hence is considerably more flowable, includingisolating the master batcher from the final mixer subject to removal ofsaid isolating and thereupon transferring said material that is to bemixed from said master batcher directly to said final mixer via theforce of gravity without intermediate storage thereof by arranging themaster batcher and final mixer in tandem one above the other to reducethe amount of space required; after master batching, cooling saidmaterial that is to be mixed in said final mixer; and during cooling andfinal mixing of a first charge in said final mixer, effecting masterbatching of a subsequent charge in said master batcher.
 2. A method incombination according to claim 1, which includes the steps of: adding,to the beginning of said final mixing stage, at least one of thematerials selected from the group consisting of polymerization agentsand reactive materials that serve for bonding on substrates; coarselydispersing said at least one material in said mixture in said finalmixer; and subsequently finely dispersing said at least one material insaid mixture in a mixing mechanism.
 3. A method in combination accordingto claim 2, which includes the step of undertaking said finelydispersing step in a double mixing screw.
 4. A method in combinationaccording to claim 1, in which said material that is to be mixed has afree surface after being transferred from said master batcher to saidfinal mixer; and which includes the steps of: adding, to the beginningof said final mixing stage, at least one of the materials selected fromthe group consisting of polymerization agents and reactive materialsthat serve for bonding or substrates; and distributing said at least oneadded material to said free surface of said material that is to bemixed.
 5. A method in combination according to claim 1, which includesthe step of effecting said transfer of said material that is to be mixedfrom said master batcher to said final mixer in such a way as to excludedust and air.
 6. A discontinuous method of producing rubber mixtures intwo stages, namely a contemporaneous master-batching stage and a finalmixing stage by combination of two mixers into a single apparatusrespectively arranged in tandem one above the other to save space, bypassing the material that is to be mixed successively through kneaders,with the maximum temperature during final mixing being less than themaximum temperature during master batching; said method in combinationcomprising the steps of:first passing the material that is to be mixedthrough a first kneader that is a ram kneader and serves as a masterbatcher having enormous power capability required to plasticize a coldrubber mixture; isolating the master-batching stage from the finalmixing stage subject to removal of said isolating and thereupontransferring said material that is to be mixed, without intermediatestorage thereof, from said first kneader directly to a second kneader,which is a ram-less kneader having a continuously open ram-less inletand serves as a final mixer having at most 30% of power of themaster-batching stage and adapted only for plasticizing the finishedmaster batch which is at approximately 100° C. and hence is considerablymore favorable; after master batching, cooling said material that is tobe mixed in said second kneader, which is larger than said firstkneader; and during cooling and final mixing of a first charge in saidsecond kneader, effecting master batching of a subsequent charge in saidfirst kneader.